Ramban on Genesis 1:6

יְהִי רָקִיעַ הַחֹמֶר הַהוֹוֶה בַּתְּחִלָּה שֶׁבְּרָאוֹ מֵאַיִן, אָמַר שֶׁיִּהְיֶה רָקִיעַ מָתוּחַ כְּאֹהֶל בְּתוֹךְ הַמַּיִם וְיִהְיֶה מַבְדִּיל בֵּין מַיִם לָמָיִם. וְשֶׁמָּא לָזֶה כִּוְּנוּ בְּאָמְרָם (ב"ר ד ב), רַב אָמַר לַחִים הָיוּ שָׁמַיִם בַּיּוֹם הָרִאשׁוֹן וּבַיּוֹם הַשֵּׁנִי קָרְשׁוּ, רָב אָמַר יְהִי רָקִיעַ יֶחֱזַק הָרָקִיעַ, רַבִּי יְהוּדָה בְּרַבִּי סִימוֹן אָמַר יֵעָשֶׂה מַטְלִית הָרָקִיעַ, כְּמָה דְּאַתְּ אָמַר (שמות לט ג) וַיְרַקְּעוּ אֶת פַּחֵי הַזָּהָב וְגוֹ': LET THERE BE A FIRMAMENT. G-d now said that the substance which had come into being first — that which He created from nought — should be a firmament, stretched as a tent in the midst of the waters, separating between waters and waters. It is possible that this is what the Rabbis intended by their saying,⁹⁶Bereshith Rabbah 4:1. “Rav said, ‘The heavens were in a fluid form on the first day, and on the second day they solidified.’ Rav thus said, ‘Let there be a firmament means let the firmament become strong.’ Rabbi Yehudah the son of Rabbi Shimon said, ‘Let the firmament become like a plate, just as you say in the verse, And they did beat — [vayerak’u contains the same root as raki’a, firmament] — the gold into thin plates.’”⁹⁷Exodus 39:3.

בְּתוֹךְ הַמָּיִם בְּאֶמְצַע הַמַּיִם, בֵּין מַיִם הָעֶלְיוֹנִים לְמַיִם הַתַּחְתּוֹנִים, כְּמוֹ שֶׁיֵּשׁ הֶפְרֵשׁ בֵּין הָרָקִיעַ לַמַּיִם שֶׁעַל הָאָרֶץ כָּךְ יֵשׁ הֶפְרֵשׁ בֵּין מַיִם הָעֶלְיוֹנִים לָרָקִיעַ, הָא לָמַדְתָּ שֶׁהֵן תְּלוּיִים בְּמַאֲמַר, בְּרֵאשִׁית רַבָּה (בראשית רבה ד':ג') וּכְתָבָהּ רַשִׁ"י (רש"י על בראשית א':ו'). וְזֶה מֵעִנְיַן מַעֲשֵׂה בְּרֵאשִׁית הוּא, וְאַל תְּקַוֶּה מִמֶּנִּי שֶׁאֶכְתֹּב בּוֹ דָּבָר, שֶׁהָעִנְיָן הוּא מִסִּתְרֵי הַתּוֹרָה. וְאֵין הַפְּסוּקִים צְרִיכִים לַבֵּאוּר הַזֶּה כִּי לֹא יַאֲרִיךְ הַכָּתוּב בְּעִנְיָנוֹ, וְהַפֵּרוּשׁ אָסוּר לְיוֹדְעָיו, וְכָל שֶׁכֵּן אֵלֵינוּ: IN THE MIDST OF THE WATERS. This means in the center of the waters, between the higher waters and the lower waters. For there is the same distance between the firmament and the waters upon the earth as between the higher waters and the firmament. Thus you may infer that the upper waters are suspended in space by the command of G-d. Thus it is explained in Bereshith Rabbah⁹⁸4:2. and in Rashi’s commentary. This is part of the process of creation [which those who know it are obliged to conceal]; so do not expect me to write anything about it, as the subject is one of the mysteries of the Torah, and the verses in their plain meaning do not require such an interpretation since Scripture itself did not go into it at length, and to give the interpretation is forbidden even to those who know it, and so much the more to us.